A conventional communications network, for example a broadband communications network comprises a plurality of physical resources, e,g. switches, cross-connects, regenerators, repeaters, transmission links such as fibre optic links or coaxial cable links, operating under control of a plurality of logical resources, e.g. transport protocols, and local controls associated with individual physical resources. The physical resources are located at a plurality of nodes or network elements and links which are distributed over a geographical area. A network operator maintains control of a communications network for its operation, administration and maintenance, utilising a management information base which stores information describing the physical and logical resources within the network. The management information base describes each network element within the network, which in a conventional network may be in the order of hundreds of individual network elements, e.g. switches, cross-connects, regenerators, each of which contains of the order of tens to hundreds of cards, having processes, line terminations, buffers, registers, switch fabrics, etc. In general, a conventional communications network may comprise a multitude of different legacy equipment types of different proprietary manufacture, each of which has its own particular internal configuration and offers its own specific capability.
The information in the management information base is used to assist the network operator to identify and locate problems within the network such as a broken transmission link or failed processor for example.
The International Telegraph and Telephone Consultative Committee (CCITT) of the International Telecommunications Union (ITU) in their Recommendation G.774 published September 1992 (available from International Telecommunications Union, General Secretariat, Sales Service, Place de Nation, Ch1211, Geneva 20, Switzerland), specifies a recommended architecture of an information model for Synchronous Digital Hierarchy (SDH) network. In Recommendation G.774, there is specified a model which describes managed object classes and their properties which are useful for describing information exchanged across interfaces to find in Recommendation M.3010, Telecommunications Network Management (TNM) architecture, also of the ITU-T. Recommendation G.774 identifies the Telecommunications Management Network (TMN) object classes required for the management of SDH network elements, and specialises the generic object classes presented in Recommendation M.3010 to provide management information specifically for synchronous digital hierarchy. These objects are relevant to information exchanged across standardised interfaces defined in Recommendation M.3010 TMN architecture. In Recommendation G.774, network resources are modelled as objects and a management view of a resource is referred to as a managed object. Objects with similar attributes may be grouped in object classes. An object is characterised by its object class and object instance, and may possess multiple attribute types and associated values. Object class is defined in Recommendation G.774 applied to various management areas, for example fault management and configuration management.
Existing methods of obtaining information and managing the synchronisation of synchronous networks rely on network elements within the network selecting the network element connected to it with the best source of synchronisation information. A number of parameters are used to determine the quality of the synchronisation information from each connected NE including the received waveform shape and the number of NE's in the synchronisation trail back to a Primary Reference Source (PRS)—a single definitive timing input into the network. Such an arrangement is described in Jamasebi UK Patent Application No. 9605013.3. WO 97/33396.
Occasionally sync problems occur on the network caused by for example an optical fibre link between NE's being broken, which results in some NE's within the network drifting off sync with the rest of the network. This problem is dealt with by interrogating the problem NE's to determine their synchronisation sources and, if appropriate, re-assign their synchronisation sources to correct the problem.